Typically, a pipeline is constructed of a number of pipe lengths or sections which are placed end to end and welded together at the respective adjacent ends as the construction of the pipeline proceeds. In order to achieve a desirable weld between the adjacent ends, the ends of the pipe sections must be clamped or held in close proximity. For this purpose, various pipe clamping apparatus have been developed for clamping the pipe sections for welding.
Once the clamping apparatus is in place, the welding is typically performed by a welding device outside of or exterior to the pipe sections. During the welding operation, a weld backup ring is preferably provided on the inside or interior surfaces of the pipe sections at the location of the abutment of the adjacent ends of the pipe sections. The backup ring is desirable for supporting the weld pool which would otherwise fall into the pipe sections during the welding operation. Also, the backup ring facilitates the formation of a relatively smooth circumferential weld internally of the pipeline.
Several conventional clamping apparatus and associated backup rings are described in United Kingdom Patent Application 2,067,945 published Aug. 5, 1981 by Rinaldi, Canadian Patent Application 2,183,156 published Aug. 17, 1995 by Brookhouse, U.S. Pat. No. 5,535,938 issued Jul. 16, 1996 to Leduc, U.S. Pat. No. 3,979,041 issued Sep. 7, 1976 to Kaneyama, U.S. Pat. No. 4,177,914 issued Dec. 11, 1979 to Clavin, U.S. Pat. No. 4,201,326 issued May 6, 1980 to Connell and U.S. Pat. No. 4,285,458 issued Aug. 25, 1981 to Slavens.
Such conventional clamping apparatus are typically capable of self-propulsion through the pipeline and include independently operable front and rear clamping mechanisms for clamping the adjacent pipe sections for welding and a backup ring for providing backup support at the weld. More particularly, the front pipe clamping mechanism comprises a plurality of clamping shoes radially movable between a retracted position and an extended position for engaging the interior surface of the front pipe section. The rear pipe clamping mechanism is also comprised of a plurality of clamping shoes radially movable between a retracted position and an extended position for engaging the interior surface of the rear pipe section.
The backup ring is similarly comprised of a plurality of segments movable between a retracted position and an extended position for engaging the interior surface of the front and rear pipes at their adjacent ends. Typically, the backup ring, is mounted with the front and rear pipe clamping mechanisms. For instance, the backup ring may either form part of, or be extendible and retractable simultaneously with, one or both of the front and rear clamping mechanisms of the associated pipe clamping apparatus.
U.S. Pat. No. 3,741,451 issued Jun. 26, 1973 to Gwin describes a relatively complex clamping apparatus which includes a backup ring which is retractable and extendible independently of the clamping mechanisms. The pipe clamping apparatus includes a clamping mechanism and a weld joint backup shoe assembly. The backup shoe assembly includes an inner torque tube rotatably mounted on a central support member. The clamping mechanism includes a pair of outer torque tubes rotatably mounted on the inner torque tube. An annular radially extending cam is mounted on each of the outer torque tubes for engagement with clamping members which are extended and retracted by movement of the associated cam. Each clamping member includes a cam follower and means for maintaining the cam follower in engagement with the associated cam. The outer torque tubes are rotated by a set of pneumatic rams in order to move the clamping members between the retracted and extended positions.
A third annular radially extending cam is mounted on the inner torque tube for engagement with backup shoes which may be extended and retracted by movement of the third cam. The backup shoes similarly include a number of cam followers and means for maintaining the cam followers in engagement with the third cam. The inner torque tube is rotated, separately or independently of the rotation of the outer torque tubes, by a separate set of pneumatic rams in order to move the backup shoe assembly between the retracted and extended positions. Thus, as stated, the structure of Gwin is relatively complex.
U.S. Pat. No. 3,937,382 issued Feb. 10, 1976 to Cunningham also permits independent operation of the weld backup. The clamping apparatus includes a first and a second set of clamping members and a weld backup mounted about a central shaft. Each of the clamping members is extended and retracted by the reciprocation of a piston coupled to the clamping members by a linkage. The weld backup includes a ring housing which defines a plurality of circumferentially spaced cylinders, each having a piston mounted therein. Each of the pistons has an end associated with a copper backup shoe. Two-way movement of each of the pistons is affected by a flow of fluid into the cylinder accommodating the piston, which results in the extension and retraction of the associated backup shoes. The operation of the pistons associated with the backup shoes is independent of the operation of the piston associated with the clamping members.
U.S. Pat. No. 5,110,031 issued May 5, 1992 to Rinaldi describes a weld supporting ring including a first crown of ring pieces (i.e., the backup shoe) and a second crown of support elements situated on either side of the first crown (i.e., the clamping mechanisms). Each ring piece of the first crown is supported by a radially extensible ring support formed by a pneumatic or hydraulic cylinder having a piston rod. Further, one end of a spring is wound about the piston rod of each ring support while the other end of the spring grips a pin mounted on an adjoining ring piece. The second crown is similarly supported by radially extensible supports consisting of pneumatic or hydraulic cylinders. The operation of the cylinders associated with the first crown appears to be independent of the operation of the cylinders associated with the second crown.
There remains a need for an actuation system which can be utilized in a pipe clamping apparatus to actuate any of a front clamping mechanism, a rear clamping mechanism or an internal backup ring system.
There also remains a need in the industry for an improved internal backup ring system for mounting between a front and rear clamping mechanism in a pipe clamping apparatus. There is a need for such a backup ring system having a relatively simple structure, which permits the operation of the backup ring system independently of the clamping mechanisms, which is relatively easily retrofittable to an existing pipe clamping apparatus, and which utilizes the front and rear clamping mechanisms to protect the internal backup ring by retracting farther than the front and rear clamping mechanisms when not in use. Finally, there is a need for a backup ring system which provides an auxiliary mechanism for the backup ring to become unstuck from the weld joint in the event such sticking occurs during the welding operation.